This invention relates to the method and apparatus for determining the weight of the vehicle and/or the cargo load based on the tire pressure and temperature.
Many different systems have been designed to measure the tire pressures of a vehicle and relay this information to the operator, see for example U.S. Pat. No. 5,675,314 issue Oct. 7 1997 to Chaklader or U.S. Pat. No. 5,289,160 issued Feb. 22, 1994 to Fiorletta. U.S. Pat. No. 4,909,074 issued Mar. 20, 1990 to Gerresheim et al. describes a specific application of sensed tire pressure wherein curves based on atmospheric temperature are used to determine safe driving conditions for the tires under the then current atmospheric conditions.
U.S. Pat. No. 5,081,443 issued Jan. 14, 1992 to Breit describes a specific tire pressure and temperature sensor and system wherein the tire pressure and temperature are both monitored as well as other outside and cab conditions. The measured tire temperature and pressure are used for two different and unrelated functions; the temperature is used to monitor the brake function while the pressure is used to monitor the weight of the cargo. The concept of measuring the weight of the vehicle based on the tire pressure has also been described in Japanese patent no. JP10267739 published Oct. 9, 1998. Inventor Tsukasa teaches that the tire pressure may be used to determine the weight of or load on a vehicle. None of the existing systems compensate for tire temperature which can significantly alter the tire pressure in determining the weight of the vehicle based on the tire pressures and thus a significant error can be included in the measured load weight obtained by practicing the teachings of the above patents of Breit and Tsukasa.
It is an object of the present invention to provide a more accurate system for measuring the weight of the vehicle and/or of its load based tire pressure. More specifically, it is an object of the present invention to provide a more accurate system for measuring the weight of the vehicle and/or of its load based tire pressure. Broadly, the present invention relates to a method for measuring the weight of a vehicle based on change in tire pressure comprising, measuring tire pressure and temperature of at least a significant number of tires on a vehicle, determining a temperature standardized pressure P(s) based on a selected standard temperature for each tire, totaling said temperature standardized pressures for said tires P(S)TOTAL and determining total weight WTOTAL of said vehicle based on
WTOTAL=CF(xcex94P(S)TOTAL)
Where WTOTAL=total weight of said vehicle
xcex94P(S)TOTAL=total or summation of all of said temperature standardized tire
pressures P(S) less the summation PI(S)TOTAL of the initial tire pressures PI 
measured with no load on the tires converted to temperature standardized
pressures PI(S) and summed to provide a summation of initial pressures
PI(S)TOTAL 
CF=a conversion factor of weight/unit change of standardized tire pressures.
Preferably, said method further comprises determining the weight of the vehicle alone WV and determining the weight of cargo WC based on
WC=WTOTALxe2x88x92WV
Preferably, said weight of the vehicle alone WV is determined by initially measuring initial tire pressure PI of each said tire under conditions of no load, determining said temperature standardized initial pressure PI(S) for said selected standard temperature for each of said tires, measuring pressure PV in said tires when said tires are subject only to the weight of the vehicle W(V) and determining a standardized pressure PV(S) for each said tire based on PV in said tires and determining weight of said vehicle WV based on the equation
WV=CF(PV(S)TOTALxe2x88x92PI(S)TOTAL)=CF(xcex94PV(S)TOTAL)
Wherein WV=Vehicle weight
PI(S)TOTAL=is the sum or total of said initial standardized pressures PI(S) for said tires under no load
PV(S)TOTAL=the sum or total of said temperature standardized pressures
PV(S) of said tires
xcex94PV(S)TOTAL=the change in total of the temperature standardized tire pressures based measured with only the weight of the vehicle over initial temperature standardized pressures under no load i.e. PV(S)TOTALxe2x88x92PI(S)TOTAL 
CF=said conversion factor of unit weight/unit change of standardized tire pressures.
Preferably, said conversion factor CF is determined by measuring said weight of the vehicle alone WV, initially measuring initial tire pressure PI of each said tire under conditions of no load, determining said temperature standardized initial pressure PI(S) for said selected standard temperature for each of said tires, measuring pressure PV in said tires when said tires are subject only to said weight of the vehicle alone W(V) and determining a standardized pressure PV(S) for each said tire based on PV in said tires and determining said conversion factor CF based on the equation
CF=WV/(PV(S)TOTALxe2x88x92PI(S)TOTAL)=WV/(xcex94PV(S)TOTAL)
Wherein WV=Vehicle weight
PI(S)TOTAL=is the sum or total of said initial standardized pressures PI(S) for said tires under no load
PV(S)TOTAL=the sum or total of said temperature standardized pressures PV(S) of said tires
xcex94PV(S)TOTAL=the change in total of the temperature standardized tire pressures based measured with only the weight of the vehicle over initial temperature standardized pressures under no load i.e. PV(S)TOTALxe2x88x92PI(S)TOTAL 
CF=said conversion factor of weight/unit change of standardized tire pressures.
Preferably, said determining said weight of cargo WC is based on the equation
WC=CF[PT(S)TOTALxe2x88x92(PV(S)TOTAL)]=CF(xcex94PC(S)TOTAL)
Wherein WC=weight of the cargo
PV(S)TOTAL=the total of said temperature standardized pressures PV(S) of said tires measure when only load on the tire is the vehicle (i.e. no load on the vehicle)
PT(S)TOTAL=the total of said temperature standardized pressures PT(S) of said tires measured under full load (i.e. vehicle plus cargo).
xcex94PC(S)TOTAL=the change in total of the temperature standardized tire pressures PT(S)TOTALxe2x88x92PV(S)TOTAL due to the weight of the cargo and
CF=said conversion factor of unit weight/unit change of standardized tire pressures.
Preferably, said determining said weight of cargo WC is based on the equation
CFTxcex94P(ST)TOTAL=CF1(xcex94P(S1))+CF2(xcex94P(S2))+CF3(xcex94P(S3))+ - - - +CFn(xcex94P(Sn))
Where xcex94P(ST)TOTAL=total of the temperature corrected changes in individual tire pressures.
CFT=a conversion factor based on change in weight/unit change of standardized tire pressures based on the weighted average of CF1, CF2, CF3 - - - CF1 and is in effect equivalent to
CFT=[CF1 (xcex94P(S1))+CF2 (xcex94P(S2))+CF3 (xcex94P(S3))+ - - - +CFn (xcex94P(Sn))]/xcex94P(ST)TOTAL CF1, CF2, CF3 - - - CFn are predetermined specific values of a conversion factor CF for each of the tires 1, 2, 3 - - - n respectively.
Preferably, said weight of the vehicle alone WV is determined by initially measuring initial tire pressure PI of each said tire under conditions of no load, determining said temperature standardized initial pressure PI(S) for said selected standard temperature for each of said tires, measuring pressure PV in said tires when said tires are subject only to the weight of the vehicle W(V) and determining a standardized pressure PV(S) for each said tire based on PV in said tires and determining weight of said vehicle WV based on the equation
WV=[CF1(PV(S1))+CF2+(PV(S2))+CF3(PV(S3))+ - - - +CFn(PV(Sn))]xe2x88x92[CF1xe2x80x2(PI(S1))+CF2xe2x80x2(PI(S2))+CF3xe2x80x2(PI(S3))+ - - - +CFnxe2x80x2(PI(Sn))]
Wherein WV=Vehicle weight
PV(S1), PV(S2), PV(S3), - - - PV(Sn)=the temperature standardized tire pressures measured with only the weight of the vehicle.
PI(S1), PI(S2), PI(S3), - - - PI(Sn)=is the respective initial standardized pressures PI(S) for each of said tires under no load.
CF1, CF2, CF3, - - - CFn are the conversion factors at the corresponding pressure PV(S1), PV(S2), PV(S3), - - - PV(Sn), respectively.
CF1xe2x80x2, CF2xe2x80x2, CF3xe2x80x2 - - - CFnxe2x80x2 are the conversion factors at the corresponding pressure PI(S1), PI(S2), PI(S3), - - - PV(Sn), respectively.
Preferably, said weight of cargo WC is determined based on the equation
WC=[CF1(PT(S1))+CF2(PT(S2))+CF3(PT(S3))+ - - - +CFn(P(Sn))]xe2x88x92[CF1xe2x80x2(PV(S1))+CF2xe2x80x2(PV(S2))+CF3xe2x80x2(PV(S3))+ - - - +CFnxe2x80x2(PV(Sn))]
Wherein WC=weight of the cargo
PT(S1), PT(S2), PT(S3), - - - PT(Sn)=the temperature standardized pressures measured under full (total) load (i.e. vehicle plus cargo).
PV(S1), PV(S2), PV(S3), - - - PV(Sn)=the temperature standardized tire pressures measured with only the weight of the vehicle.
CF1, CF2, CF3, - - - CFn are the conversion factors at the corresponding pressure PT(S1), PT(S2), PT(S3), - - - PT(Sn), respectively.
CF1xe2x80x2, CF2xe2x80x2, CF3xe2x80x2 - - - CFnxe2x80x2 are the conversion factors at the corresponding pressure PV(S1), PV(S2), PV(S3), - - - PV(Sn), respectively.